The disclosure concerns a method for controlling a color printer or a color copier in which, with the aid of a printing unit, at least one color separation of a first color and a color separation of a second color are applied on a printing substrate to be printed to in order to generate a print image, and in which—with the aid of a control field printed by the printing unit of the color printer or, respectively, color copier—a control signal of a control is established to reduce the registration error between the color separation of the first color and the color separation of the second color.
Given multicolor printing, multiple color separations are printed atop one another on the printing substrate to generate the color image. In particular, four color separations are printed atop one another, namely cyan, yellow, magenta and black. In order to obtain a print image of high quality, it is necessary that the individual color separations are printed atop one another precisely as intended, since otherwise color deviations and/or blurring can occur. The deviations with which the individual color separations are printed relative to one another are designated as registration errors or register errors.
A known method to reduce registration errors is that control markings of the different colors of the color separations are printed in an edge region of the printing substrate and it is visually determined whether a registration error is present, and how large this is. The control of the printing unit is adapted accordingly. What is problematic in this method is that, due to the manual determination of the registration error, this can only take place in a quite imprecise manner, and a large expenditure is required for this.
In an alternative method, the printed control markings can be detected with the aid of an optical, high-resolution sensor, and the registration error can be determined from these automatically. In this case, the control of the printing unit is also thereupon adapted such that the registration error is reduced or, optimally, no registration error at all is present anymore. With this method it is problematic that expensive high-resolution optical sensors are necessary for this. These special sensors are also used exclusively to determine the registration error, and must be able to measure at various points over the print format.
Methods to determine registration errors are known from the documents DE 10 2009 035 006 A1, DE 102 44 437 B4, U.S. Pat. No. 7,396,099 B2, DE 101 31 957 A1, DE 10 2010 036 249 A1, US 2010/0007690 A1, U.S. Pat. No. 7,184,700 B2, DE 32 48 795 C2, EP 1 593 508 A2 and DE 197 38 992 A1, for example. A method to detect optical printing variables in multicolor production printing is known from the document DE 196 39 014 C2.
From the document DE 43 35 350 A1, a method is known for determining registration deviations given multicolor printing in which a REAL color value of a measurement field is determined and compared with a DESIRED color value. The desired color value is determined with the aid of an o.k. curve or with the aid of repro data. This has the disadvantage that the desired color value can only be calculated very imprecisely, and thus the registration control can likewise only take place in a very imprecise manner.